To realize digital cash, you require a payment network with accounts, balances and transactions. One problem that every payment network has to solve, is to prevent that one entity spends the same amount twice. This is usually done by a central server who keeps record of the balances. CORUSBLOCK runs within a decetralized network. There is no central server. Every entity within the network is required to do this job. Any peer in the network needs to have a list with all transactions, to check whether future transactions are valid. This is a so-called peer-to-peer network.